CDATASection

CDATA sections are used to escape blocks of text containing characters that
would otherwise be regarded as markup. The only delimiter that is
recognized in a CDATA section is the "]]>" string that ends the CDATA
section. CDATA sections cannot be nested. Their primary purpose is for
including material such as XML fragments, without needing to escape all
the delimiters.

The CharacterData.data attribute holds the text that is
contained by the CDATA section. Note that this may contain characters that need to be escaped outside of CDATA sections and
that, depending on the character encoding ("charset") chosen for
serialization, it may be impossible to write out some characters as part
of a CDATA section.

The CDATASection interface inherits from the
CharacterData interface through the Text
interface. Adjacent CDATASection nodes are not merged by use
of the normalize method of the Node interface.

No lexical check is done on the content of a CDATA section and it is
therefore possible to have the character sequence "]]>"
in the content, which is illegal in a CDATA section per section 2.7 of [XML 1.0]. The
presence of this character sequence must generate a fatal error during
serialization or the cdata section must be splitted before the
serialization (see also the parameter "split-cdata-sections"
in the DOMConfiguration interface).

Note: Because no markup is recognized within a
CDATASection, character numeric references cannot be used as
an escape mechanism when serializing. Therefore, action needs to be taken
when serializing a CDATASection with a character encoding
where some of the contained characters cannot be represented. Failure to
do so would not produce well-formed XML.

Note: One potential solution in the serialization process is to
end the CDATA section before the character, output the character using a
character reference or entity reference, and open a new CDATA section for
any further characters in the text node. Note, however, that some code
conversion libraries at the time of writing do not return an error or
exception when a character is missing from the encoding, making the task
of ensuring that data is not corrupted on serialization more difficult.

Puts all Text nodes in the full depth of the sub-tree
underneath this Node, including attribute nodes, into a
"normal" form where only structure (e.g., elements, comments,
processing instructions, CDATA sections, and entity references)
separates Text nodes, i.e., there are neither adjacent
Text nodes nor empty Text nodes.